This application claims the priority of German Patent Application Serial No. 101 14 846.1, filed Mar. 24, 2001.
The present invention relates, in general, to a clutch release bearing, and more particularly to a clutch release bearing for use in a clutch mechanism for motor vehicles.
A clutch release bearing is typically intended for actuation of a clutch mechanism, e.g. separating clutch, disposed between the internal combustion engine and a gearbox, and is configured as a tapered roller bearing which includes a non-rotatable outer bearing ring, a revolving inner bearing ring, and rolling members, received in a cage and guided between the bearing rings. Operatively connected to the inner ring is an adjustment ring, which establishes a connection between a disk spring of the clutch mechanism and the release bearing. The adjustment ring is configured to allow a relative movement of the adjustment ring and the inner ring so as to implement a self-adjusting or self-aligning release bearing.
Such a release bearing is able to compensate shocks generated by axial misalignment with the disk spring that is connected directly to the clutch mechanism. The axial misalignment, caused by the disk spring, increases wear and thus reduces the service life of the release bearing and triggers the so-called clutch judder that adversely affects the overall riding comfort.
German Pat. No. DE 72 45 141 U describes a release bearing which includes an adjustment ring disposed between the disk spring or arms of the disk spring of the clutch mechanism and the inner ring of the release bearing. The contact zone between the adjustment ring and the inner ring is hereby configured with complementing spherical surfaces of the adjustment ring and the inner ring so as to allow a relative movement and alignment between these structural parts. The inner ring and the adjustment ring are designed as massive parts which are made through a material-removing process and expensive and require a fairly large space for installation.
German Pat. No. 199 12 432 A1 describes a self-aligning release bearing with a revolving inner ring. Provided between the disk spring or arms of the disk spring of the clutch mechanism and the inner ring is an adjustment ring, which together with the inner ring is supported by complementary calotte-shaped segments. The bearing rings of the release bearing as well as the adjustment ring are made through a deep-drawing process without material removal.
Common to both, German Pat. No. DE 72 45 141 U and German Pat. No. 199 12 432 A1, is the fact that the adjustment ring and the inner ring are made of same material. As a consequence, rust formation caused by friction can be experienced, resulting in greater wear, so that the service life of these release bearings is insufficient to meet the demands by vehicle manufactures.
It would therefore be desirable and advantageous to provide an improved release bearing, which obviates prior art shortcomings and which exhibits a long service life, is maintenance-free and cost-efficient to produce while still being reliable in operation to effectively dampen or compensate axial misalignments, to prevent clutch judder.
According to one aspect of the present invention, a release bearing includes a rolling-contact bearing having a non-rotatable outer ring, a rotating inner ring, and plural rolling members located between the outer and inner rings; an adjustment ring having a ring flange for abutment against a disk spring of a clutch mechanism; and a sliding element made of bearing material and disposed in a support zone defined between the inner ring and the adjustment ring and configured in the form of complementary calotte-shaped portions so that the adjustment ring and the inner ring are movable relative to one another for effecting a self-adjustment of the release bearing.
The present invention resolves prior art problems by providing a sliding element in the contact zone between the adjustment ring and the revolving inner ring of the release bearing. As a result of the reduction in friction, the self-adjusting feature of the components, inner ring and adjustment ring, is significantly improved. The optimized self-adjustment is further able to significantly dampen the axial shocks generated by the disk spring or arms of the disk spring as a result of axial oscillations of the internal combustion engine and transmitted via the clutch mechanism into the release bearing.
According to another feature of the present invention, the sliding element may be made of a bearing material or a suitable friction-reducing and wear-resistant material to ensure a maintenance-free and long service life. Thus, a direct support of the inner ring and the adjustment ring, which are both made of steel, is prevented. By sandwiching the sliding element in the support zone between the inner ring and adjustment ring, the latter components are effectively decoupled from one another so that noise development is suppressed and friction-based rust formation as well as clutch judder is prevented. The sliding element can be connected to either one of the carriers, i.e. inner ring or adjustment ring, without requiring any modification of the carrier that is selected to bear against the sliding element, so that existing installation space can be used.
It is to be understood by persons skilled in the art that the term xe2x80x9ccarrierxe2x80x9d is used in the following description to refer to the inner ring of the release bearing or to the adjustment ring.
The wear of the spherical contact zones of the sliding elements by the inner ring and the adjustment ring is comparably small. The sliding element can be produced in great numbers cost-efficiently and requires no particular handling for installation and attachment to the inner ring of the release bearing or the adjustment ring. The securement of the sliding element can be implemented in any suitable manner known to the artisan and includes force-fitting and/or positive connections. During operation, the sliding element separates the inner ring of the release bearing from the adjustment ring and allows a maintenance-free self-adjustment between the inner ring and the adjustment ring. The self-adjustment, which is realized at low friction and exhibits damping characteristics at the same time, is implemented with little wear and may be effected together with a self-alignment in radial direction.
According to one embodiment of the present invention, the sliding element may be connected to the adjustment ring. A largest possible contact surface can be realized, when the sliding element embraces the entire side of the adjustment ring, directed to the inner ring of the release bearing. In this way, a direct contact between the inner ring and the adjustment ring is prevented, even at extremely tilted positions. The support of the sliding element over a large area improves further the securement of the sliding element to the adjustment ring. As an alternative, the sliding element may also be connected over a large area to the inner ring of the release bearing at the side facing the adjustment ring. In either case, the large-area contact of the sliding element upon the adjustment ring or inner ring results in a sufficient support in each and every position, i.e., also when the adjustment ring occupies an extremely tilted disposition. At the same time, the large-area contact of the sliding element ensures a reduced surface pressure so that the strength and rigidity of the sliding element is not adversely affected.
According to another feature of the present invention, the sliding element may also be configured in segments to thereby improve the adhesion of the sliding element because tension as a consequence of different coefficients of thermal expansion between the carrier, i.e. adjustment ring or inner ring, and the sliding element is effectively eliminated. Of course, the sliding element may also be configured with at least one longitude slot, which coincides with the symmetry axis, in order to compensate varying coefficients of thermal expansion. Instead of one slot, also several slots may be provided about the circumference of the sliding element, whereby the slots may be formed alternately on the inside or outside of the sliding element. Any suitable configuration of the slot or slots is conceivable, i.e., straight, meander-shaped or slanted.
The production costs for making a sliding element according to the present invention can be reduced, when employing an injection molding process. This process can also be used to incorporate in a single step the slots and grooves in the sliding element for compensation of varying coefficients of thermal expansion. The injection molding process may have sprue gates or a cone gate so that the sliding element can be made with a same strength essentially throughout.
Regardless of its configuration, the sliding element may be positively secured to either one of the carriers, i.e. inner ring of the release bearing or the adjustment ring. Suitably, the surface of the carrier may be formed with grooves for engagement of projections of the sliding element. As a result, the sliding element is also secured against rotation. As an alternative, the sliding element may be urged into a forced engagement to the carrier, for example, through gluing. An example of a suitable glue includes a high-temperature adhesive. Gluing of the sliding element ensures also a compensation of even small unevenness between the carrier and the sliding element so as to prevent the formation of voids which are detrimental to a secure attachment of the sliding element.
According to another feature of the present invention, the sliding element may be formed by a coating applied directly through injection onto the inner ring or adjustment ring. In this way, diametrical tolerances of the mating components, inner ring and adjustment ring, that may influence the structural length, are eliminated. Suitably, the carrier may include in the contact zone with the sliding element a circumferential crease or groove, which is filled by the material of the sliding element during injection molding, to realize an effective securement of the sliding element to the carrier. In this way, the need for an additional separate securement of the sliding element is eliminated. Stress through shrinkage during injection molding can be counteracted in a controlled manner, by providing the inner ring or the adjustment ring in the support zone with at least one axis-parallel or helical notch. To prevent a rotation of the parts, a groove is provided in diametric opposition to the notch and also filled with sliding element material during injection molding.
The sliding element, on the one hand, and the inner ring or the adjustment ring, on the other hand, may be made of different materials. The material for the sliding element is selected by taking into account optimum wear properties and friction properties as well as inexpensive fabrication and mounting to the inner ring or adjustment ring. The carrier, inner ring or adjustment ring, forms a unitary structure with the sliding element and is suitably made of steel. The configuration of the carrier allows hereby a production without material removal, in particular a deep-drawing process that enables a production of the adjustment ring as well as of the inner ring on a large scale in a cost-efficient manner. A sufficient strength, especially wear-resistance, can be realized, at least in those zones that are subject to high loads, such as the calotte-shaped segments, tracks for the rolling members, or contact surface for support of the arms of the disk spring of the clutch mechanism, through respective heat-treatment.
The sliding element is suitably made of a high-strength and wear-resistant plastic, such as thermoplastic material or a duroplastic material. The sliding element may include additives such as carbon fibers, MoS2, PTFE and/or epoxy resins, alone or in combination, for realizing a lubrication and/or improved service life, when the sliding element is based on duroplastic material. The use of duroplastic material significantly enhances the useful life of the sliding element, without adversely affecting the manufacturing costs. The sliding element may also be made of PPA or PA46 combined with carbon fibers as wear-reducing agent and PTFE as friction-reducing agent. Its may also be conceivable to make the sliding element of ceramic material. This ceramic material, also called industrial ceramic, exhibits optimal wear-resistance and is therefore suitable for use with a contact surface that is subject to severe conditions and soiling during operation of the release bearing.
The adjustment ring may be made by a deep-drawing process and is suitably made of steel C80M which subsequently can be hardened through heat-treatment.
Persons skilled in the art will understand, that the foregoing description of materials for the sliding elements is not exhaustive but only illustrative, because other materials or material combinations may be conceivable as well so long as they generally follow the concepts outlined here, i.e. exhibit sufficient friction properties and wear-resistance and can be shaped appropriately and manufactured in a cost-efficient manner.
According to another feature of the present invention, the relative movement between the adjustment ring and the inner ring of the release bearing may be limited by providing the sliding element with a collar to form a stop between the components to be moved. Suitably, the collar is formed in one piece onto the sliding element and extends in parallel relationship to a ring flange of the adjustment ring, when installed. In an extreme position, the collar also prevents the adjustment ring from a support upon the outer contour of the inner ring.
As an alternative to the single-piece configuration of the adjustment ring with radially directed ring flange, for support of the disk spring of the clutch mechanism, and calotte-shaped segment to complement the inner ring, the disclosure also covers an assembled adjustment ring. Such an adjustment ring includes a radial ring flange, preferably made of steel, for direct attachment of the sliding element, made for example of plastic. Suitably, the sliding element is made from a duroplastic material by an injection tool drawn in axial direction to provide a N-section profile. The use of duroplastic material is advantageous here because of its sufficient strength and shape stability. The sliding element may be secured to the ring flange through gluing in combination with protrusions for positive engagement in respective recesses of the ring flange. A two-part design allows an optimal material selection that can be best suited to the function of the ring flange and the sliding element and combined to a unitary structure.
The assembled adjustment ring may also be made of components of same material. For example, the adjustment ring may be made of ceramic material or duroplastic material. The single parts of the adjustment ring can be glued in the bore area of the flange and thus permanently connected together. Examples of positive connections between these two parts include a crown gearing and/or spline profiles or the like, whereby a greater contact surface is realized at the same time. In addition, the adjustment ring is secured against rotation and the bonding of the parts is improved. Excess adhesive can be accumulated in depressions or notches formed on at least one bonded surface of the annular regions being joined. As the adjustment ring is composed of parts of same material, the coefficient of thermal expansion is of no concern here. At the same time, the two-part configuration decreases manufacturing costs. The approximately axially aligned region of the adjustment ring, provided for reinforcement for the sliding element, is omitted and results to on optimization of the component.
The adjustment ring may also have a single-piece configuration and be made of duroplastic material or ceramic, to further optimize the component.
According to another feature of the present invention, all components of the release bearing are captivated after mounting and installation, by so configuring an end portion of the sliding element or a leg portion of the adjustment ring as to engage in an annular groove or recess in the elastic housing with play so as to radially overlap an outer contour of a housing wall of the annular groove. Thus, the housing can be joined together and captivated with the release bearing and the adjustment to form a prefabricated unitary structure.
According to another feature of the present invention, a seal is received in the form of a labyrinth seal between the sliding element, the housing and the inner ring of the release bearing. The sliding element has one end which points to the guide sleeve and has a projection which forms with a wall portion of the annular groove and/or a seal for the guide sleeve a labyrinth-like gap, for realizing an improved sealing of the release bearing.
According to another feature of the present invention, the calotte-shaped portions of the inner ring and the sliding element are disposed at an angle of xe2x89xa720xc2x0 to an axis of symmetry of the release bearing. Suitably, the sliding element and the inner ring have a radius of xe2x89xa725 mm in the area of the contact surface.
According to another feature of the present invention, the release bearing is self-adjusting, wherein the outer ring has an annular skirt which is guided on a retention element, mounted non-rotatably on the housing, for displacement in an axial direction. A radial displacement between the release bearing and the housing is thus precluded.